Philippe Gabant

Alpha-fetoprotein protects the developing female mouse brain from masculinization and defeminization by estrogens

Two clearly opposing views exist on the function of alpha-fetoprotein (AFP), a fetal plasma protein that binds estrogens with high affinity, in the sexual differentiation of the rodent brain. AFP has been proposed to either prevent the entry of estrogens or to actively transport estrogens into the developing female brain. The availability of Afp mutant mice (Afp−/−) now finally allows us to resolve this longstanding controversy concerning the role of AFP in brain sexual differentiation, and thus to determine whether prenatal estrogens contribute to the development of the female brain. Here we show that the brain and behavior of female Afp−/− mice were masculinized and defeminized. However, when estrogen production was blocked by embryonic treatment with the aromatase inhibitor 1,4,6-androstatriene-3,17-dione, the feminine phenotype of these mice was rescued. These results clearly demonstrate that prenatal estrogens masculinize and defeminize the brain and that AFP protects the female brain from these effects of estrogens.

Alpha-fetoprotein, the major fetal serum protein, is not essential for embryonic development but is required for female fertility

The alpha-fetoprotein gene (Afp) is a member of a multigenic family that comprises the related genes encoding albumin, alpha-albumin, and vitamin D binding protein. The biological role of this major embryonic serum protein is unknown although numerous speculations have been made. We have used gene targeting to show that AFP is not required for embryonic development. AFP null embryos develop normally, and individually transplanted homozygous embryos can develop in an AFP-deficient microenvironment. Whereas mutant homozygous adult males are viable and fertile, AFP null females are infertile. Our analyses of these mice indicate that the defect is caused by a dysfunction of the hypothalamic/pituitary system, leading to anovulation.

Alpha-fetoprotein controls female fertility and prenatal development of the gonadotropin-releasing hormone pathway through an antiestrogenic action

ABSTRACT It has been shown previously that female mice homozygous for an alpha-fetoprotein (AFP) null allele are sterile as a result of anovulation, probably due to a defect in the hypothalamic-pituitary axis. Here we show that these female mice exhibit specific anomalies in the expression of numerous genes in the pituitary, including genes involved in the gonadotropin-releasing hormone pathway, which are underexpressed. In the hypothalamus, the gonadotropin-releasing hormone gene, Gnrh1, was also found to be down-regulated. However, pituitary gene expression could be normalized and fertility could be rescued by blocking prenatal estrogen synthesis using an aromatase inhibitor. These results show that AFP protects the developing female brain from the adverse effects of prenatal estrogen exposure and clarify a long-running debate on the role of this fetal protein in brain sexual differentiation.

The art of selective killing: Plasmid toxin/antitoxin systems and their technological applications

Most bacterial strains harbor plasmids that are maintained with remarkable stability. A large variety of plasmids encode systems that act when other control mechanisms have failed, i.e., when plasmid-free progeny is generated during replication. The mechanisms that control plasmid maintenance by T/A loci are well known: the antagonistic regulators that neutralize the toxins are metabolically unstable. Rapid depletion of these unstable regulators occurs in newborn, plasmid-free cells. As the same cells have inherited stable toxin molecules from the mother cell, the toxin will no longer be neutralized by the antitoxin, leading to the killing of the plasmid-free cells. This mechanism effectively reduces the proliferation of plasmid-free cells in growing bacterial populations (1). The most widely studied T/A system so far is the ccd system located on the F plasmid (2). The ccd system is composed of two genes, ccdA and ccdB, encoding small proteins: the CcdA antidote (8.7 kDa) and the CcdB toxin (11.7 kDa). The CcdB protein acts as a poison because it selectively targets the Escherichia coli DNA gyrase, a bacterial topoisomerase II. Early studies of this T/A system were performed at the Universite Libre de Bruxelles (ULB). Today new applications are commercialized by Delphi Genetics SA, a spin off company of the ULB founded by the researchers who developed the use of T/A systems as selectable markers. POSITIVE SELECTION VECTORS

Stimulation of the α-fetoprotein promoter by unliganded thyroid hormone receptor in association with protein deacetylation

alpha-Fetoprotein (AFP) is a serum protein expressed during fetal life, the expression of which is shut off after birth. The activity of the mouse Afp gene promoter region comprised between -80 and -38 bp is regulated by the thyroid hormone receptor (T3R): negatively in the presence of T3 and positively in the absence of T3. The stimulating effect of unliganded T3R is, unexpectedly, antagonized by cofactors that have histone-acetyl-transferase activity, or by sodium butyrate, which inhibits histone acetylases (HDACs). The unliganded T3R stimulating activity effect is thus associated with protein deacetylation, contrary to the usual situation. In combination with previous results, our observations suggest that T3-mediated down regulation of the Afp promoter is due to T3-induced protein acetylation leading to loss of a nucleosomal structure (required for promoter activity) and chromatin opening.

Rat Chromosome 2: assignment of the genes encoding cyclin B1, interleukin 6 signal transducer, and proprotein convertase 1 to the Mcs1-containing region and identification of new microsatellite markers

Abstract. The rat Chromosome (Chr) 2 harbors several genes controlling tumor growth or development, blood pressure, and non-insulin-dependent diabetes mellitus. We report that the region (2q1) containing the mammary susceptibility cancer gene Mcs1 also harbors the genes encoding cyclin B1, interleukin 6 signal transducer (gp130), and proprotein convertase 1. We also generated 13 new anonymous microsatellite markers from Chr 2-sorted DNA. These markers, as well as a microsatellite marker in the cyclin B1 gene, were genetically mapped in combination with known markers. A cyclin B1-related gene was also cytogenetically assigned to rat Chr 11q22-q23.

Molecular analysis of RepHI1B, a replicon specific to IncHI1 plasmids

RepHI1B is one of the replicons that is specific to IncHI1 multireplicon plasmids. Its general organization resembles that of several replicons that control their copy number by an iteron mechanism. The RepHI1B replicon (2.4 kb) contains: (i) an 882 bp repA gene coding for a 32 kDa replication protein (RepA), sharing significant similarity with the initiator proteins of other replicons belonging to various incompatibility (Inc) groups, including P1 (IncY), Rts1 (IncT), RepFIB (IncFI), and RepHI1A (IncHI1); (ii) two sets of 17 bp DNA repeats (iterons), one upstream and one downstream from repA. By complementation testing, we identified the replication origin (ori) of RepHI1B in a 223 bp locus upstream from repA. By primer extension we mapped two promoters of repA (Pr1 and Pr2) in the ori sequence. We used repA::lacZ transcriptional fusions to study regulation of the repA gene. This analysis showed that repA is transcriptionally autoregulated. Gel mobility shift assays demonstrated that RepA binds specifically to the origin and to iterons overlapping the Pr1 and Pr2 promoters. A G to A transition at nucleotide position 13 of the iteron located in Pr2 (repeat 5) drastically decreases autoregulation of repA by inhibiting binding of RepA.